1. Field of the Invention
The present invention relates generally to apparatuses and methods for transmission and reception in a codebook based Closed-Loop (CL) Multiple Input Multiple Output (MIMO) system. More particularly, the present invention relates to apparatuses and methods for generating an optimum codebook and communicating using the optimum codebook.
2. Description of the Related Art
In response to increasing demands for high-speed and high-quality data transmission, a Multiple Input Multiple Output (MIMO) technique using a plurality of transmit antennas and receive antennas is drawing a lot of attention as one solution for satisfying those demands. The MIMO technique conducts a communication using a plurality of channels by means of multiple antennas, to thus drastically enhance a channel capacity, compared to a single-antenna system. For example, when a transmitter and a receiver use M-ary transmit antennas and M-ary receive antennas, channels between the antennas are independent of each other, and bandwidth and total transmit power are fixed, the average channel capacity increases by M times the single antenna.
The MIMO technique can be classified into an Open-Loop (OL)-MIMO and a Closed-Loop (CL)-MIMO based on feedback. According to the CL-MIMO, the transmitter receives channel information fed back from the receiver. There are two feedback methods. First, the receiver quantizes and feeds back a channel coefficient value to the transmitter. This method features a quite accurate value relative to the channel of the transmitter but suffers considerable feedback overhead. Secondly, the receiver refers to a codebook with an estimated channel and feeds back the retrieved codebook index to the transmitter, which can reduce the feedback overhead.
When the codebook is used in the CL-MIMO system, factors affecting the system performance include the codebook design, the codebook type, the codebook size and the like. Thus, in the codebook based MIMO system, it is necessary to design an optimum codebook by properly setting causes according to a purpose (e.g., channel capacity increase, average error rate reduction, codebook search complexity reduction and the like).
Therefore a need exists for an apparatus and method for generating an optimum codebook in a codebook based CL-MIMO system.